1. Field of the Invention
The invention relates mainly to the field of the holding of machining workpieces on work tables, and in particular, to the field of negative pressure clamps.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
During machining, assembly or transformation operations on workpieces it is necessary for the workpiece to be firmly fixed to a support. This fixing, commonly known as a clamp, nowadays no longer has jaws and has evolved to allow the shaping of complex and sometimes very large-sized workpieces such as, for example, panels or sheets, made of highly varying materials (wood, metal, polymer, composite, etc).
The clamps required by industry have to meet varying constraints.
In many applications, the workpiece that is to be held has dimensions and shapes that do not remain constant during the holding operation and so the clamp has to allow highly varied machining workpieces to be positioned and held in position, and this also means that the surface via which the workpiece is fixed in the clamp has to deliver a holding force that remains constant whatever the size and geometry of the workpiece, and also that the workpiece has to be identified precisely in a direction perpendicular to the surface of the clamp.
Another known constraint in producing and designing clamps is that the holding operation has to be performed under conditions that are optimal from the point of view of the time needed, either to maneuver the workpiece between two configurations of the clamp, or to switch workpieces between the workpiece already shaped and a workpiece still to be machined, for example on a production, cutting, drilling, grinding, etc. The operation of holding and of releasing the machining workpiece, and the reverse process between positioning the workpiece and immobilizing it, has to be performed in the shortest possible space of time for obvious productivity reasons.
Various known devices described, for example, in patent EP 1 283 760 in the name of the applicant company or patent EP 1 082 196 which discusses a system for the negative pressure fixing of panels for machining by means of pistons, or even document EP 505 668 which describes suction-cup means for immobilizing workpieces, address the following problems inadequately, if at all: the workpiece has to be immobilized and released in the shortest possible space of time; in order to be inserted easily into an automated transformation line, the holding device must not impede access to the machining workpieces; the energy consumption must be minimal; the clamp must be able to hold flat workpieces of varying sizes with complex contours, but must also be able to hold workpieces of complex shape, which are not flat, and in that respect the tools currently available are particularly ill-suited; the clamp must be able to position the machining workpiece accurately.
Just like the negative pressure clamps known from the prior art, the device that addresses the abovementioned problems has also to meet the general constraints on this type of tool, namely satisfactory distribution of the suction pressure across the work surface and optimal shutting-off of the points not covered by the surface that is to be held, while at the same time ensuring that the method operates at low cost.
It is therefore an objective of the invention to address these key difficulties by proposing a new clamp operating on negative pressure suction.
The prior art discloses devices operating by negative pressure suction for holding workpieces or objects.
In documents U.S. Pat. No. 3,335,994 A and U.S. Pat. No. 3,197,170 A, the suction devices are devices with shut-off balls used to shut off or open the outlet of the suction ducts of the cavities situated under a support plate. These devices are complex to implement, with numerous components that have to be assembled and difficulties in achieving a reliable seal between the balls and the workpiece support plate.
Document DE 3 140 882 A discusses a suction device the suction cavities of which each open via several orifices in a support plate, it being possible for said orifices to be shut off by deformable lamellae. This device has the same disadvantages as the previous ones.
In order to obviate the difficulties of operation of devices with shut-off balls or lamellae, the applicant company has leaned toward a solution that employs a flexible membrane by way of shut-off means.
The prior art cites patent U.S. Pat. No. 4,221,356 A which describes a suction-cup device configured for holding workpieces and not for the precise holding that machining entails. However, the suction cup described certainly presents a problem of operation because, as it deforms, it may come into contact with the bottom of the suction chamber, leading to a risk of canceling the suction force and causing the workpiece to fall.
The prior art also discloses another device discussed in document DE 92 04 704 U1 and which employs a flexible membrane by way of a means of shutting off the suction ducts that open into chambers situated under said membrane.